Just How Disgusting Is That Used Car?

Matt Jancer

Apr 2, 2018

Bryan Regan

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From the April 2018 issue

The smart used-car buy is a vehicle into which the owner has poured his heart and soul. But whether it’s heart and soul, tender loving care, or outright neglect, every car receives something else from its owner: hair, skin flakes, fingernail trimmings, and worse. A used car can be like an accidental archaeological dig. A 2015 University of Nottingham study examined 15 daily drivers and found evidence of potential E. coli, a bacteria in fecal matter famous for food poisoning, and Staphylococcus, of which certain subtypes can cause serious skin infections. Another study conducted in 2016 by a microbiologist at the University of Salford, Manchester, concluded that our cars can be more than 22 times grodier than that smartphone you use to scroll through Instagram in the bathroom.

To see for ourselves just how vile the average used car is, we asked a pair of microbiologists from the University of North Carolina at Greensboro, Dr. Robert Cannon and Laura Fondario-Grubbs, to bring their sterile swabs and join us at a used-car lot. Not a CarMax or a certified-preowned-car lot, either, but one of those dingy stores erected inside a chain-link cage. In each of our five randomly selected test vehicles, Cannon and Fondario-Grubbs swabbed the driver’s seat, steering wheel, radio controls, driver’s floor mat, and trunk. At the end of the day, their swabs black with filth, they took the samples back to the UNCG’s lab.

The results were not what we’d expected. Most of the cars showed a fair amount of typical harmless bacteria, the kind that covers everyday objects; but tests for the really nasty alarmist stuff, like E. coli and Staph, came back negative in all five vehicles. Turns out, cars sitting unused in a parking lot are far from giant Petri dishes; they’re actually very hostile to germs, Cannon tells us.

“Cars show a microbiome of the persons who drive them,” he says. But how long bacteria survive depends on temperature, humidity, and whether they can suck up water and food to reproduce. Humans and the stuff we bring with us into our cars—willingly and otherwise—are a major source of nutrients for these microorganisms. If nobody is using the car, nobody is restocking their food supply, so the bacteria start to die off. Parked in direct sunlight during summer, a car’s interior can reach above 170 degrees. On a frigid winter day, it’ll be as cold as the snow on its hood. Both extremes are inhospitable to a lot of common bacteria.

That the cars in Nottingham’s and Salford’s studies were driven daily is critical. Without a human bringing germs and nutrients into the cabin on a regular basis, that microbiome depopulates rapidly. Because it’s not the cars that are gross, it’s us.

So Rank

For our experiment, swabs from the vehicles were used to inoculate Petri dishes containing three growth media. In order of increasing filth, the swabbed areas ranked as follows:

Bryan Regan

Disclaimers: Yes, we know that not all bacteria are bad. And our sample size is vanishingly small. Car and Driver is not a scientific journal. Just go with it.